title: The small GTPase RhoB regulates TNFα signaling in endothelial cells.
abstract: The inflammatory response of endothelial cells triggered by cytokines such as TNFα and IL1β plays a pivotal role in innate immunity. Upon pro-inflammatory cytokine stimulation, endothelial cells produce chemokines and cytokines that attract and activate leukocytes, and express high levels of leukocyte adhesion molecules. This process is mediated by intracellular signaling cascades triggered by activation of e.g. the TNFα receptor (TNFR) that lead to the activation of the NFκB transcription factor and of MAP kinases, which in turn activate inflammatory gene transcription. We found that the small GTPase RhoB was strongly and rapidly upregulated in primary human endothelial cells by TNFα, IL1β and LPS. We subsequently investigated the role of RhoB in the regulation of TNFR signaling in endothelial cells by silencing RhoB expression with siRNA. We provide evidence that the TNFα-induced activation of p38 MAP kinase is strongly dependent on RhoB, but not on RhoA, while JNK activation is regulated by both RhoB and RhoA. Consistent with the important role of p38 MAP kinase in inflammation, we demonstrate that loss of RhoB impairs TNFα-induced ICAM-1 expression and reduces cell production of IL6 and IL8. In addition, we show that RhoB silencing alters the intracellular traffic of TNFα after endocytosis. Since RhoB is a known regulator of the intracellular traffic of membrane receptors, our data suggest that RhoB controls TNFα signaling through the regulation of the TNFR traffic.
authors.affiliation: Department of Molecular Cell Biology, Sanquin Research and Landsteiner Laboratory, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Kroon
authors.forename: Simon
authors.initials: S
authors.lastname: Tol
authors.forename: Sven
authors.initials: S
authors.lastname: van Amstel
authors.forename: Judith A
authors.initials: JA
authors.lastname: Elias
authors.forename: Mar
authors.initials: M
authors.lastname: Fernandez-Borja
mesh_terms: D004705:Endocytosis / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D020868:Gene Silencing / Q000187:drug effects; D061307:Human Umbilical Vein Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism* / Q000494:pharmacology; D020743:rhoB GTP-Binding Protein / Q000378:metabolism*
chemical_list: D018836:Inflammation Mediators; D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D020928:Mitogen-Activated Protein Kinases; D020743:rhoB GTP-Binding Protein